When is the indirect object pronoun required in sentences with an indirect object?jrdioko -> No; that's correct. Because is a different scenario: There you are using a subject ("tu biblioteca"), whilst in the question, we are talking about using it with pronouns ("mi,ti, etc."). You could even say "Pertenece a mi persona", since "mi persona" would be the subject. That's correct, because there you are using "mi" (as opposite to "mí") as determinative possessive. Notice the difference between "MI" and "MÍ"